If you are in your 40's or you are over that, what suggestion do you have for a man in his 30's?

If you're single, travel.

Plan where you want to go carefully.
Let people know where you are; when you intend to leave a destination and when you hope to arrive by.
Keep a diary. Write letters and take photos. Produce a blog. Sample food; architecture; music; theatre; art.....everything !

Then come home and write the book 😀